Chucks used to rotationally support tools are commonly known. Chucks are usually attached to a power drill and are generally of the 3 jaw type which are adjustable to allow clamping of different diameter tool shanks. Drill bits are most commonly clamped in a chuck and are typically long and cylindrically shaped, having a round shank at one end for mounting in a chuck and at the opposite end a cutting face. Drill bits vary in diameter depending on the size hole to be drilled and are commonly available in very small diameters through to larger diameters.
A problem when using chucks to clamp a drill bit is slip. This occurs during the drilling process as the chuck jaws tend to slip around the shank causing damage. This results in both salient and recessed radial grooves on the shank which can cause operational problems including out of true rotation and weakening of the shank. Chucks can also over tighten and jam closed making release of the chuck and drill bit removal difficult continually operating a chuck is also time consuming with drill bit changeovers.
Other drill bits have hexagonal shanks which may be inserted into a corresponding hexagonal cavity of a mandrel. The mandrel fits into a three jaw chuck and the hexagonal cavity in the mandrel both supports the drill bit and acts as a rotational drive means. Although useful in connecting drill bits without having to operate a three jaw chuck each time, the arrangement is prone to run-out. Run-out occurs as the drill bit experiences radial variation along its longitudinal axis during rotation.
This is seen by the user as rotational wobble from side to side when looking along the length of the drill bit this wobble makes it difficult for a user to drill a hole accurately when drilling into various materials, in particular metals. Drill bit starts are also very difficult into for example sheet metal.
One of the main reasons for this run-out is that hexagonal shafts and bores are generally mass produced and the accuracy in regard to straightness along their length as well as dimensional accuracy is difficult to maintain compared to round bores and shafts. This lack of straightness of the bore and shaft as well as play between the bore and shaft when fitted together, result in levels of run-out that, whilst acceptable for some tools, is an unacceptable level of run-out for drills, as any run-out of the mandrel is amplified across the longer length of a drill resulting in large run-out at the drill cutting face.
A further problem is that hex chucks accept only one size shank. This is generally [¼]″ which is suitable for drills of smaller diameter. Larger diameter drills require heavier rotational forces and support making the [¼]″ shaft inadequate. One could have two chucks to adapt to two different shank sizes, one chuck for smaller diameter drills and another chuck for larger diameter drills but this would require changeover of chucks which is cumbersome.
What is needed therefore is a quick change chuck assembly and suitable tools which overcomes one or more of the aforementioned problems and provides the public with a useful alternative.